TOKYO (AP) -- Mount Usu, a volcano on Japan's northern Hokkaido island, is in danger of erupting following a series of tremors related to volcanic activity, the Meteorological Agency warned Tuesday.

The agency issued an emergency volcano warning at 2:50 a.m. after the number and size of quakes increased around the base of the 2,416-foot mountain.

Three towns with a combined population of 51,300 are near the mountain. While each town is monitoring the volcano and has notified residents of the possible danger, none has issued orders to evacuate, spokesmen for each said.

''The tremors are occurring more frequently but there's still no indication of movement in the volcano's magma that would lead to an eruption,'' said Katsuhiro Morita, a spokesman for Date city, located about four miles from the volcano.

The Meteorological Agency said it recorded as many as 30 quakes in an hour, the same number normally registered in a month. Some of the quakes were big enough to be felt by humans.

The mountain, located about 42 miles southwest of Sapporo, last erupted in 1978, killing two and destroying 196 homes, said Takaharu Kiriyama, a spokesman for the National Land Agency.

The National Land Agency is charged with gathering information and disseminating it to the appropriate government bureaucracies, Kiriyama said. Orders to evacuate the towns rests with the respective local governments.

Sapporo is located about 520 miles northwest of Tokyo.